Experimental comparison of different minichannel geometries for use in evaporators

Ağartan, Yiğit Ata
This thesis investigates the refrigerant (R-134a) flow in three minichannels having different geometries experimentally. During the last 40 years heat transfer in small scales has been a very attractive research area. Improvements in heat transfer in the refrigeration applications by means of usage of micro/minichannels provide significant developments in this area. Also it is known that experimental studies are very important to constitute a database which is beneficial for new developments and research. During the two-phase flow experiments conducted in the minichannels, low mass flow rates and constant wall temperature approach, which are the conditions in the evaporators of the refrigerator applications were applied because one of the purposes of this study is to determine the most ideal minichannel among the tested minichannels for usage in the evaporator section of the refrigerators. Two-phase flow experiments were made with refrigerant R134a in the three minichannels having hydraulic diameters of 1.69, 3.85 and 1.69 mm respectively. As distinct from the others, the third minichannel has a rough inner surface. Comparison of the experimental results of the three minichannels was made in terms of forced convection heat transfer coefficients and pressure drop at constant quality and mass flux values. As a result of the experiments, the most ideal minichannel among the tested minichannels was determined for the evaporator applications in the refrigerators.


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This thesis investigates the refrigerant (R-134a) flow in a minitube experimentally. The small scale heat transfer is a relatively new research area and has been in favor since the end of 1970’s. Refrigerant flow in mini- and microscale media is a potential enhancement factor for refrigeration technology in the future. For the forthcoming developments and progresses, experimental studies are invaluable in terms of having an insight and contributing to the establishment of infrastructure in the field in addi...
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The thermal characterization of aluminum flat grooved heat pipes is performed experimentally for different groove dimensions. Three heat pipes with groove widths of 0.2 mm, 0.4 mm, and 1.5 mm are used in the experiments. The effect of the amount of the working fluid is extensively studied for each groove width. The results reveal that, although all three succeed in dissipating the heat input through the phase change of the working fluid by continuous evaporation and condensation, the effectiveness of the he...
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Using Landau mean field model, the spontaneous polarization and the dielectric susceptibility are analyzed as functions of temperature and pressure close to the cubic-tetragonal (ferroelectric-paraelectric) transition in BaTiO3. From the analysis of the dielectric susceptibility and the spontaneous polarization, the critical exponents are deduced in the classical and quantum limits for BaTiO3. From the critical behavior of the dielectric susceptibility, the spontaneous polarization can be described for the ...
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Ayli, Ece; Bayer, Özgür; Aradağ Çelebioğlu, Selin (2016-11-01)
Steady-state heat transfer from rectangular fin arrays is examined experimentally and numerically for turbulent fully developed flow. The effects of geometrical parameters on heat transfer coefficient and Nusselt number are investigated. For different inter fin ratios, Reynolds number and Nusselt number dependence of the results is investigated. A generalized empirical correlation for Nusselt number is developed for rectangular fins for a Reynolds number range of 17 x 10(7) < Re < 2.47 x 10(8), and an aspec...
Origin of forward bias capacitance peak and intersection behavior of C and G/w of Ag/p-InP Schottky barrier diodes
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Frequency-dependent electrical characteristics of Ag/p-InP diodes have been determined using impedance spectroscopy at room temperature. Series resistance (R,) and interface state(s) (N-ss) values were extracted from capacitance (C) and conductance (G/w) data using the Nicollian and Goetzberger and Hill-Coleman methods, respectively. C and G/w data were also corrected in the whole measured bias voltage range to obtain real diode capacitance C-c and conductance G(c) values in order to see the effects of R-s....
Citation Formats
Y. A. Ağartan, “Experimental comparison of different minichannel geometries for use in evaporators,” M.S. - Master of Science, Middle East Technical University, 2012.